1886.] The Harmonic Analyser at the Meteorological Office, 387 



Conveniently placed in the machine is a cylinder or drum, the 

 circumference of which is equal to the length of twenty-four -hours 

 upon the thermograms. Round this cylinder the thermograms are 

 rolled, the fluctuations of temperature indicated by the curves being 

 followed, as the cylinder revolves, by a combination of the move- 

 ment of the cylinder with that of a pointer moving in a line parallel 

 to its axis. 



The handle by which the cylinder is turned gives motion at the 

 same time to the seven disks of the machine, and the operator thus 

 controls by his left hand both the speed with which the curves are 

 paid through the machine and the consequent velocity of the angular 

 motion of the disks, while by a suitable contrivance, the movements 

 of the pointer, governed by his right hand and following the curve, 

 produce on the face of the disks corresponding movements to the right 

 or left of the balls by which the motion of the disks is conveyed to 

 the recording cylinders. 



At the commencement of an operation all the cylinders are set to 

 zero ; the twelve months curves are then passed consecutively through 

 the instrument ; the first pair of cylinders, which gives the coefficients 

 of the first order, and also the mean cylinder, 7, being read for each 

 day, while cylinders 3 and 4, and 5 and 6, which give the coefficients 

 of the second and third orders respectively, are only read for each five 

 days and at the end of each calendar month. The numbers on the 

 cylinders are, however, progressive, so that the increments upon them 

 for any given period could very easily be obtained. The form in which 

 the readings are recorded is as follows : — 



Readings of the Recording Cylinders of the Harmonic Analyser. 

 Dry-bulb Thermometer Curves, from July 30 to August 3, 1882. 

 Kew Observatory. 



Month and day. 



First order. 



Cylinder 1. 



Cylinder 2. 



Reading at 

 midnight. 



Difference 

 from last 

 reading. 



Reading at 

 midnight. 



Difference 

 from last 

 reading. 





+ 10-480 





-12 333 





„ 31 



„ 2 



„ 3 



+ 12 -540 

 + 12-678 

 + 12-773 

 + 12-814 

 + 12 -807 



+ 0-103 

 + 0-138 

 + 0-095 



+ o -oti 



+ 0-083 



-14-926 

 -15-004 

 -15-069 

 -15-207 

 -15 287 



-0-118 

 -0-078 

 -0-065 

 -0188 

 -0-080 



